1. Field of the Invention
This invention relates to a window, for example a window for a waveguide for a beam of electromagnetic radiation.
2. Discussion of the Background
Electromagnetic radiation, and more particularly microwave radiation, is generated in gyrotrons and other high power microwave sources. A beam of the radiation is generated and this passes along a waveguide to an exit port. The waveguide comprises a passage, generally of circular cross-section, having a window extending across it. The beam of electromagnetic radiation passes through the window. The window is used for the protection of the electromagnetic sources or detectors from environmental factors. The window may be made of a variety of materials such as sapphire, diamond and the like. Such windows are generally planar, although curved profiles have been suggested.
According to the present invention, a window for a waveguide for a beam of electromagnetic radiation, comprises a layer of a material capable of allowing electromagnetic radiation to pass therethrough and a support on each side of the layer, each support defining a passage for electromagnetic radiation, and the layer being provided with at least one recess formed in the periphery thereof.
Preferably a plurality of recesses are formed in the periphery of the layer, those recesses preferably being evenly spaced around the periphery. The number of recesses will vary according to the nature of the layer and will typically exceed six.
The depth of the recess or recesses into the layer will vary according to the nature of the material from which the layer is made, the size and shape of the layer and other such factors. For example, where the layer is disc-shaped, the depth of the recess or recesses may be chosen to reduce the peak level of hoop stresses in the layer.
In one form of the invention, each support is located inside the periphery of the layer and the or each recess has a depth equal to or less the distance of the supports from the periphery.
It is preferred that each recess is free of sharp corners, e.g. has a rounded end which extends into the layer.
Each support may take the form of a ring having a flange which bears against a surface of the layer. The flanges will generally extend outwards and away from the passage defined within the supports. To minimise expansion of the flanges, a retaining ring may be provided around the outwardly extending flanges. The retaining ring may be made of a material such as molybdenum.
The supports will generally be bonded to a surface of the layer by means of a braze or diffusion bond. The layer may take any suitable shape such as rectangular, but will generally be disc-shaped.
The material from which the layer is made will typically be sapphire, diamond, germanium, zinc selenide, silicon, doped silicon, silicon nitride, aluminium nitride or boron nitride. The window is preferably made of diamond. Such diamond is preferably produced using chemical vapour deposition (CVD).
The invention extends to a layer for use in a window as described above, such layer being of a material capable of allowing electromagnetic radiation to pass therethrough and being provided with at least one recess formed in the periphery thereof.